High capacity smokeless flare having a very low gas flow detector

ABSTRACT

A method and at least one gas flare for carrying out or practicing the method are disclosed for smokeless burning of undesired gas. The new full range, high capacity steam aspirating gas flare comprises a steam control system responsive to the new very low gas flow detector utilizing a knockout drum water seal having an end of the main line submerged therein with two bypass lines around the main line end for detecting various gas flows in the unmeasurable ranges below 3 percent of the maximum design gas flow and for controlling steam flow to the flare (1) to insure a smokeless flame and (2) to provide high savings in steam usage.

.llnited States Patent 1191 Stranahan etal.

1451 Dec. 3, 1974 HIGH CAPACITY SMOKELESS FLARE HAVING. A VERY LOW GAS FLOW DETECTOR [73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 19, 1973 21 Appl. NO.Z 426,267

Related US. Application Data [63] Continuation-impart of Ser. No. 266,795, June 27,

1974, abandoned.

[56] References Cited UNITED STATES PATENTS 2,761,496 9 1956 'Verner et al 431 4 x 2,779,399 l/l957 Zink et al. 1. 431/90 2,891,607 6/1959 Webster et a] 431/90 3,322,178 5/1967 Nahas 431/202 X 3,779,689 12/1973 Reed et al 431/89 Primary Examiner-Charles .l. Myhre Assistant Examiner-William C. Anderson Attorney, Agent, or FirmT. H. Whaley; C. G. Ries 5 7 ABSTRACT A method and atleast one gas flare for carrying out or practicing the method are disclosed for smokeless burning of undesired gas. Thenew full range, high capacity steam aspirating gas flare comprises a steam control system responsive to the new very low gas flow detector utilizing a knockout drum water seal having an end of the main line submerged therein with two bypass lines around the main line end for detecting various. gas flows in the unmeasurable ranges below 3 percent of the maximum design gas flow and for controlling steam flow to the flare (l) to insure a smokeless flame and (2) to provide high savings in steam usage.

14 Claims, 1 Drawing Figure HIGH CAPACITY SMOKELESS FLARE HAVING A VERY LOW GAS FLOW DETECTOR BACKGROUND OF THE INVENTION This invention is a continuation-in-part of our prior patent application Ser. No. 266,795, filed June 27, 1972, now abandoned.

The government requires the burning of all excess gases being admitted to the atmosphere. The collection of these gases is normally put into a flare line which is equipped with a pilot light to insure the burning of all gases.

Recent regulations require that this burning be smokeless in order to reduce air pollution.

Because of the wide range of gas flow going to a given flar'e (from minimum to maximum) the velocity of gas flow in the gas line is so low at times that the conventional differential flow measuring meters are not ade quate to cover the full range.

In another flare control system, as in US. Pat. No. 2,891,607, when the gas flow became low, a steam control system injected steam at the top of the flare in proportion to gas flow. In addition to that gas, an additional continuous supply of fuel gas is admitted to the flare to insure a combustionable mixture in the flare. This latter supply of fuel gas is very wasteful and obviated by the instant invention.

Accordingly, to cover this immeasurable gas flow range, the usual practice is either (1) to use no steam for aspirating air to the flare and letting it smoke when in this range or (2) to use the same amount of steam as required for the lowest measurable flow rate, the latter using farmore steam than actually is required and accordingly involves needless wasting of steam.

OBJECTS OF THE INVENTION A primary object of this invention is to provide a method for burning unwanted gas at all operating ranges without polluting the air with smoke.

Another object of this invention is to provide a method for detecting and burning unwanted gases in the low flow rate ranges which are immeasurable in the main gas line.

A further object of this invention is to provide a smokeless flare that operates with gases having a flow rate well below that rate that can be measured by the conventional gas flow rate pitot venturi detector.

A still further 'object of this invention is to provide a very low gas flow detector for a high capacitysmokeless flare.

Still another object of this invention is to maintain a flare smokeless with a minimum amount of steam usage.

Another object of this invention is to provide a gas flare for efficiently and smokelessly burning gas having an immeasurable flow rate in its large main gas line to the flare, the immeasurable flow rate gas having a slow flow rate portion and a very slow flow rate portion.

Another object of this invention is to provide a smokeless flare that is easy to operate, is of simple configuration, and is economical to form and assemble.

Other objects and various advantages of the disclosed method and smokeless flare for carrying out the method will be apparent from the following detailed description together with the accompanying drawings, submitted for purposes of illustration only, and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims. 7

The drawing diagrammatically illustratesby way of example, not by way of limitation, a smokeless flare.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic diagram of a very low gas flow detectorfor a high capacity smokeless flare with parts in section.

METHOD OF MAINTAINING A GAS FLARE SMOKELESS The invention comprises a method for maintaining a gas flare smokeless utilizing an aspirating steam nozzle when the gas flow in the main gas line is less than that which the conventional flow meter can measure. This immeasurable flow rate range may be divided into two portions, a slow flow rate portion and a very slow flow rate portion. The method comprises:

1. detecting gas that is flowing at the slow flow rate portion of the immeasurable flow rate range of gas flow in the main gas line,

2. detecting gas that is flowing at the very slow flow rate portion of the immeasurable flow rate range,

3. varying the amount of steam to the aspirating steam nozzle equal to an empirically determined set amount of steam when the gas flow rate is at least in the very slow flow rate portion for providing a smokeless air-to-gas mixture, and

4. adding a second empirically determined fixed set amount of steam to the aspirating steam nozzle when the gas flow rate reaches the slow flow rate portion for providing a smokeless air-to-gas mixture and for conserving steam.

More specifically, for use with a gas flare for burning gas that has passed through a liquid separator including a container of liquid and gas wherein the main gas sup ply line protrudes well below the surface of the liquid for preventing flame travel in the gas line, the first two steps may include:

a. passing the gas through a first bypass line around the submerged end of the main gas supply line into the container to a shallower predetermined depth,

b. passing the gas through a second bypass linc around the submerged end of the first bypass line into the container to-a shallower predetermined depth than the first bypass line,

c. detecting gas flow through the second bypass line, which flow would indicate that the flow in the main gas supply line is at least in the very slow or immeasurable flow rate portion.

While only two flow rate ranges in the immeasurable range in the main gas line are described in the instant method and flare for carrying out the method, other numbers of ranges may be utilized if so required by the particular operating requirements.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention disclosed herein, the scope of which being defined in the appended claims is not limited in its application to details of construction and arrangement of parts shown and described, since the invention is capable of other embodiments and of being practiced or carried out in various other ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The FIGURE discloses a steam aspirating gas flare and the new very low gas flow detector 11 designed for maintaining a smokeless flame, typical gas flares being illustrated in US. Pat. Nos. 2,761,496; 2,779,399; and 2,891,607. The flare control system may be a conventional system or like one disclosed in Assignees patent application Ser. No. 192,453, filed Oct. 26, 1971, entitled Smokeless Gas Flare which comprises two portions, one portion for very low gas flow rates in which the rate is too low for accurate measuring and a second portion for all other varying flow rates. The present very low gas flow detector is an improvement over Assignees prior detector disclosed in the patent application, particularly in that while Assignees prior detector was designed for the present day gas flare, the disclosed gas flare detector is designed for improving the present day flares and for high capacity gas flares of the near future.

IMPROVED GAS FLARE SYSTEM The flare 10 comprises a conventional steam aspirating gas flare in which steam, or any other gas, is blown through an aspirating nozzle to pull in air for mixing with the unwanted gas to be burned in the atmosphere. A preferred gas flare is disclosed in Assignees aboveidentified patent application wherein the steam is controlled through a steam control system for the various flow rates of gas flow to provide the proper steam-togas ratio for each gas flow rate for accordingly producing the correct air-to-gas mixture in the flare burner to insure a smokeless flame.

VERY LOW .GAS FLOW DETECTOR The very low gas flow detector 11, in the FIGURE comprises a water seal or knockout drum 12 to which the main gas supply line 13 has an end 14 submerged deep in the drum, a first bypass line 15 around the end portion of the main gas supply line having an end 16 submerged to a lesser amount in the drum, and a second bypass line 17 around the first bypass line and having an end 18 submerged to a shallower depth than that of the first bypass line. Baffle 19 in the drum is provided to maintain a desired level in the seal section of the drum.

Exit main gas line 13b carries all gas from the drum that enters the drum from the main gas supply line and the two bypass lines to the gas flare via a conventional steam control system, or one as disclosed in Assignees above-identified patent application for providing the proper steam-to-gas ratio for all measurable gas flow rates. The disclosed detector 11 provides the proper steam-to-gas ratio for all immeasurable gas flow rates as dictated by the very low gas flow detector 11. In the second portion of the main flare supply line 13b is a conventional rate of flow detector 20, as a pitot venturi detector, and conventional steam control system 20a for providing the proper two, empirically determined steam-to-gas ratios for the various or two disclosed ranges of immeasurable gas flow as detected in the main gas supply line.

First bypass line 15, of the FIGURE has an orifice run 21 for detecting the gas flow therethrough the smaller line with flow transmitter 22 for transmitting this flow rate information to the flare and its conventional steam control system for supplying an empirically determined fixed set amount of steam to the aspirating nozzle to provide a smokeless flare. The diameter of this first bypass line is designed sot that the maximum flow therethrough is the minimum measurable flow in the large line to the flare. This is slightly over 3 percent of the maximum design flow of the gas to the flare.

Second bypass line 17, has an orifice run 23 for detecting gas flow and flow transmitter 24 for signalling the flare and its steam control system for supplying steam to the aspirating nozzle at an empirically determined set steam-to-gas ratio to provide a smokeless flame.

In actual use, while the main gas supply line 13 may be 42 inches in diameter, and its lower end 14 submerged about 36 inches, first bypass line 15 may be 10 inches in diameter with its outer end 16 submerged 16 inches and second bypass line 17 may be 6 inches in diameter with its outer end submerged about 8 inches below the surface of the liquid. Because of the varying depths of gas line outlets l4, l6, and 18 in liquid separator drum 12, the lowest gas flow rate portion passes from the shallowest outlet 18 of bypass 17, the next higher flow rate portion of the immeasurable gas passes from the next deeper outlet 16 of bypass l5, and all remaining gas in the higher and measurable flow rate ranges passes from the deepest outlet 14 of the main gas supply line 13a.

With any gas flow in the main gas supply line in the first 3 percent of design maximum flow range being immeasurable by the conventional flow rate meter 20, the lowest flow rate is detected in bypass line 17. When the flow rate becomes too large to be detected in this line by flow transmitter 24 the seal in line 15 will blow and the higher rate will be detected in line 15 by flow transmitter 22. The second bypass line 17 may be set for detecting gas flow in a first portion of the immeasurable flow rate range as, for convenience, the first onethird of 3 percent or greater than 0 to 100 range of design maximum flow. The flow transmitter 24 of the second bypass line 17 then causes an empirically determined fixed set amount of steam to enter the flare to insure a smokeless air-to-gas mixtures for this first flow rate portion.

The empirically determined fixed steam rate for this very low gas flow rate portion as detected by second bypass line 17 is that which is found to maintain the flare smokeless at the upper limit of gas flow in this very low flow rate range portion. This steam-to-gas ratio may be set between 1 to 0.1 to l to 10 depending on the specific gravity of the particular gas, the ratio of l to 1 being most common approximate ratio utilized. The fixed amount of steam so required to maintain this flow rate range portion smokeless is approximately one-third the amount of steam required for burning gas having the minimum measurable rate of flow as measured in main line 13b. The first bypass line 15 would flow is accordingly controlled to an empirically determined fixed set amount for providing the proper steamto-gas ratio at the aspirating flare nozzle for producing a smokeless air-to-gas mixture for burning in the flare.

Likewise, because there is not a constant steam-togas ratio that will provide a smokeless flame over the full operating range of flare gas flow, the conventional or disclosed variable steam control system provides a smokeless flame or smokeless flare over the full range of gas that can be detected in the main gas supply line 13b and above the empirically'set amount required by the very low gas flow rate detector 11 described above.

OPERATION Accordingly in operation of the flare and its very low gas flow rate detector 11, when the gas flow is in the very low gas flow rate portion of the immeasurable gas flow rate range which is unmeasurable by the conventional flow rate pitot venturi meter 20 in main gas supply line 13b, flow of gas then only passes through bypass line 17, its exit 18, the shallowest exit, drum 12, and main supply line 13b to the flare aspirating steam nozzle. A smokeless air-to-gas mixture is produced at the flare by an empirically determined set amount of steam injected through the aspirating steam nozzle as controlled by the flow meter 24 and orifice run 23 of smallest and shallowest bypass line 17.

As the gas pressure and flow rate increase in the main supply line to reach the low flow rate portion of the immeasurable gas flow rate range, gas then flows through larger and deeper bypass line 15, its exit 16, drum 12, main gas line 13b to the flare. A smokeless airto-gas mixture is produced at the flare by the additional empirically determined set amount of steam being injected through the flare aspirating steam nozzle in proportion to the gas flow as detected in the bypass 15 with its orifice run 21 and flow transmitter 22.

Likewise, as the gas flow reaches and/or goes beyond the minimum measurable amount as detected by detector in main supply gas line 13b, additional steam is caused to flow to the aspirating steam nozzle in proportion to the gas flow in-the main supply line 13b as controlled by the conventional or known steam control sy stern 20a. 1

Each of the very low immeasurable gas flow rate, the low immeasurable gas flow rate, and the measurable gas flow rate detectors overlap at the extremities of their respective ranges to insure continuous and uninterrupted steam flow control.

Accordingly a reliable and efficient steam control system results for measuring, metering, and supplying the proper amount of steam to the flare for maintaining the proper air-to-gas ratio and resultant smokeless flare in all ranges of gas flow from the immeasurable, but detectable, flow to the maximum flow.

In practice, while no method is provided here for differentiating between high and low molecular weight hydrocarbons, a steam rate of about 0.35 pounds of steam per pound of hydrocarbon is the minimum to allow for the heaviest hydrocarbons.

Thus, it will be seen that the instant gas flare for covering the full operating ranges of gas flow provides a smokeless flame in a manner which meets each of the objects set forth above.

While a method and a smokeless gas flare for carryfrom the scope of the invention, and it is accordingly desired to comprehend within the purview of this invention such methods and modifications as may be considered to fall within the scope of the appended claims.

We claim:

1. A method for maintaining an aspirating steam nozzle gas flare smokeless wherein the gas is supplied to the flare from a large main gas line with a low flow rate which is immeasurable in the large main gas line, the immeasurable flow rate gas range comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, comprising the steps of,

a. detecting gas that is flowing at the slow flow rate portion of l percent to 3 percent of maximum design flow rate of the immeasurable flow rate range,

b. detecting gas that is flowing at the very slow flow rate portion of up to 1 percent maximum design flow rate of the immeasurable flow rate range,

, c. varying the amount of steam to the aspirating steam nozzle equal to an empirically determined fixed set amount of steam when the gas flow rate is at least in the very slow flow rate portion for providing a smokeless air-to-gas mixture, and

(1. adding a second empirically determined fixed set of steam to the aspirating steam nozzle when the gas flow rate reaches the slow flow rate portion for providing a smokeless air-to-gas mixture and for conserving steam.

2. A method as recited in claim 1 wherein the gas from the main supply line passes through a liquid separator including a container of liquid and gas with the end of the main gas line protruding well below the surface of the'liquid for preventing flame travel in the gas line, the first two steps including further,

a. passing the gas through a first bypass line around the submerged end of the main gas line into the container to a shallower predetermined depth,

b. passing the gas through a second bypass line around a submerged end of the first bypass line into the container to a shallower predetermined depth than that of the first bypass line,

' c. detecting gas flow through the second bypass line, which flow indicates that flow in the main gas line is at least in the very slow flow rate portion, and

d. detecting gas flow through the first bypass line, which flow indicates that the flow in the main gas line is at least in the slow flow rate portion.

3. A method as recited in claim 2 wherein an end of the large main gas line is submerged deep in a drum of liquid from which the gas is supplied to the flare, the fourth step of detecting gas flow comprises further,

a. submerging the end of the first bypass gas line shallower in the drum of liquid than the main gas line end for detecting the slow flow rate portion of gas from the main line.

4. A method as recited in claim 2 wherein the third step of detecting gas flow comprises further,

a. submerging an end of the second bypass gas line shallower in the drum of liquid than the end of the first bypass gas line for detecting the very slow flow rate portion of gas from the main line.

5. A method for maintaining an aspirating steam nozzle gas flare smokeless wherein the gas is supplied to the flare through a large main gas line and has a flow rate which is immeasurable in the large main gas line, the immeasurable flow rate gas comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to l percent maximum design flow rate, comprising the steps of,

a. submerging an end of the large main gas line deep in a container of liquid,

b. bypassing the submerged end of the large main gas line with a first bypass gas line having an end submerged shallower in the container than the main gas line submerged end,

0. bypassing the end of the first bypass gas line with a second bypass gas line having an end submerged shallower in the container than the first bypass gas line submerged end,

d. detecting any gas flow in the second bypass line for indicating gas in the main line is flowing at least as fast as the very slow flow rate of up to 1 percent maximum design flow rate,-and

e. detecting any gas flow in the first bypass line for indicating gas in the main line is flowing as fast as the slow flow rate of 1 percent to 3 percent of maximum design flow rate.

6. The method as recited in claim 5 comprising further the steps of,

a. varying the amount of steam to the aspirating steam nozzle for maintaining an empirically determined set ratio of steam-to-gas ratio for providing a smokeless gas-to-air' mixture when gas flows through the second bypass gas line, and

b. adding an empirically determined fixed set amount of steam to the aspirating steam nozzle for maintaining an empirically determined set steam-to-gas ratio for providing a smokeless gas-to-air mixture when gas flows through the first bypass gas line.

7. A method for smokeless burning of unwanted gas in a flare supplied with air from a gas aspirating nozzle wherein the unwanted gas is supplied to the flare in a large main gas line and has a variable flow rate from a measurable flow rate-range down to an immeasurable flow raterange in the main gas line, the immeasurable flow rate range comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, comprising the steps of,

a. passing the unwanted gas through a first bypass line around the large main gas line to the flare for detecting the gas flow slow flow rate portion of 1 percent to 3 percent of maximum design flow rate,

b. passing the unwanted gas through a second bypass line around the first bypass line for detecting the gas flow very slow flow rate portion of up to l percent maximum design flow rate, and

c. passing the unwanted gas through the main line for detecting any gas flow in the measurable flow rate range.

8. A smokeless gas flare having an aspirating steam nozzle for mixing air with gas for burning wherein the gas flow has an immeasurable flow rate in a large main gas line to the flare, the immeasurable flow rate gas having a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare further comprising,

a. a first bypass line means around an end of the main gas line for passing the gas flow slow flow rate portion of 1 percent to 3 percent of maximum design flow rate,

b. a second bypass line means around an end of said first bypass line means for passing the gas flow very slow flow rate portion of up to 1 percent maximum design flow rate,

c. first means on said first bypass line means for detecting gas flowing at the slow flow rate,

d. second means on said second bypass line means for detecting gas flowing at the very slow flow rate,

e. means responsive to said first means for adding an empirically determined fixed set amount of steam for providing a smokeless flame, and

f. means responsive to said second means for adding a second empirically determined fixed set amount of steam for providing a smokeless flame.

9. In a gas flare for burning gas that has passed through a liquid separator including a container of liquid and gas wherein the main gas supply line protrudes well below the surface of the liquid for preventing flame travel in the gas line and wherein the gas flow has an immeasurable flow rate in the main gas supply line to the flare, the immeasurable flow rate gas having a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, means for detecting the flow rates comprising,

a. a first bypass line between the main gas supply line and the container,

b. a second bypass line between the first bypass line and the container,

c. said first bypass line having means for detecting gas at the slow flow rate portion of l percent to 3 percent of maximum design flow rate, and

(1. said second bypass line having means for detecting gas at the very slow flow rate portion of up to l percent maximum design flow rate.

10. A smokeless gas flare wherein the gas flow has an immeasurable flow rate in a large main gas line to the flare, the immeasurable flow rate gas having a slow flow rate portion of l percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare further comprising,

a. first means for detecting gas flowing at the slow flow rate of 1 percent to 3 percent maximum design flow rate,

b. second means for detecting gas flowing at the very slow flow rate of up to 1 percent maximum design flow rate,

c. third means responsive to said first means for adding an empirically determined fixed set amount of steam for smokeless burning of the slow flow rate gas, and

d. said third means being responsive to said second means for adding a second empirically determined fixed set amount of steam for smokeless burning of the very slow flow rate gas.

11. A smokeless gas flare as recited in claim 10 wherein,

a. said first detecting means comprises an orifice run means on a first bypass line around an end of the large main gas line for detecting the slow flow rate portion of gas flow, and

b'. said second detecting means comprises an orifice run means on a second bypass line around'an end of the first bypass line for detecting the very slow flow rate portion of gas flow.

'12. A smokeless gas flare as recited in claim 11 wherein an end of the large main gas line is submerged deep in a drum of liquid from which the gas is supplied to the flare and wherein,

a. said end of said first bypass line is submerged shallower in said drum of liquid than themain gas line end for passing the slow flow rate portion of gas, and

b. an end of said second bypass line is submerged shallower in said drum of liquid than said first bypass line end for passing the very slow flow rate portion of gas.

13. A smokeless gas flare utilizing aspirating steam for mixing air with gas for burning wherein-the gas is supplied to the flare in a large main gas line and has a flow rate which is immeasurable in the large main gas line at times, the immeasurable flow rate gas comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare comprising further,

a. first means for detecting gas in the gas flow slow flow rate of 1 percent to 3 percent of maximum design flow rate,

b. second means for detecting gas in the gas flow very slow flow rate of up to 1 percent maximum design flow rate, 5

0. means for controlling aspirating steam flow to the gas flare for each of the ranges, and

(1. each of the steam flow controlling means being responsive to its respective detecting means for its range for maintaining a smokeless flame in the flare as the gas flow rate varies in the immeasurable flow rate portions.

14. A smokeless gas flare as recited in claim 13 wherein,

a. said first detecting means comprises an orifice run means on a first bypass line around an end of the large main gas line for detecting the slow flow rate portion of gas flow, and

b. said second detecting means comprises an orifice run means on a second bypass line around an end of the first bypass line for detecting the very slow flow rate portion of gas flow. 

1. A method for maintaining an aspirating steam nozzle gas flare smokeless wherein the gas is supplied to the flare from a large main gas line with a low flow rate which is immeasurable in the large main gas line, the immeasurable flow rate gas range comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, comprising the steps of, a. detecting gas that is flowing at the slow flow rate portion of 1 percent to 3 percent of maximum design flow rate of the immeasurable flow rate range, b. detecting gas that is flowing at the very slow flow rate portion of up to 1 percent maximum design flow rate of the immeasurable flow rate range, c. varying the amount of steam to the aspirating steam nozzle equal to an empirically determined fixed set amount of steam when the gas flow rate is at least in the very slow flow rate portion for providing a smokeless air-to-gas mixture, and d. adding a second empirically determined fixed set of steam to the aspirating steam nozzle when the gas flow rate reaches the slow flow rate portion for providing a smokeless air-to-gas mixture and for conserving steam.
 2. A method as recited in claim 1 wherein the gas from the main supply line passes through a liquid separator including a container of liquid and gas with the end of the main gas line protruding well below the surface of the liquid for preventing flame travel in the gas line, the first two steps including further, a. passing the gas through a first bypass line around the submerged end of the main gas line into the container to a shallower predetermined depth, b. passing the gas through a second bypass line around a submerged end of the first bypass line into the container to a shallower predetermined depth than that of the first bypass line, c. detecting gas flow through the second bypass line, which flow indicates that flow in The main gas line is at least in the very slow flow rate portion, and d. detecting gas flow through the first bypass line, which flow indicates that the flow in the main gas line is at least in the slow flow rate portion.
 3. A method as recited in claim 2 wherein an end of the large main gas line is submerged deep in a drum of liquid from which the gas is supplied to the flare, the fourth step of detecting gas flow comprises further, a. submerging the end of the first bypass gas line shallower in the drum of liquid than the main gas line end for detecting the slow flow rate portion of gas from the main line.
 4. A method as recited in claim 2 wherein the third step of detecting gas flow comprises further, a. submerging an end of the second bypass gas line shallower in the drum of liquid than the end of the first bypass gas line for detecting the very slow flow rate portion of gas from the main line.
 5. A method for maintaining an aspirating steam nozzle gas flare smokeless wherein the gas is supplied to the flare through a large main gas line and has a flow rate which is immeasurable in the large main gas line, the immeasurable flow rate gas comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, comprising the steps of, a. submerging an end of the large main gas line deep in a container of liquid, b. bypassing the submerged end of the large main gas line with a first bypass gas line having an end submerged shallower in the container than the main gas line submerged end, c. bypassing the end of the first bypass gas line with a second bypass gas line having an end submerged shallower in the container than the first bypass gas line submerged end, d. detecting any gas flow in the second bypass line for indicating gas in the main line is flowing at least as fast as the very slow flow rate of up to 1 percent maximum design flow rate, and e. detecting any gas flow in the first bypass line for indicating gas in the main line is flowing as fast as the slow flow rate of 1 percent to 3 percent of maximum design flow rate.
 6. The method as recited in claim 5 comprising further the steps of, a. varying the amount of steam to the aspirating steam nozzle for maintaining an empirically determined set ratio of steam-to-gas ratio for providing a smokeless gas-to-air mixture when gas flows through the second bypass gas line, and b. adding an empirically determined fixed set amount of steam to the aspirating steam nozzle for maintaining an empirically determined set steam-to-gas ratio for providing a smokeless gas-to-air mixture when gas flows through the first bypass gas line.
 7. A method for smokeless burning of unwanted gas in a flare supplied with air from a gas aspirating nozzle wherein the unwanted gas is supplied to the flare in a large main gas line and has a variable flow rate from a measurable flow rate range down to an immeasurable flow rate range in the main gas line, the immeasurable flow rate range comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, comprising the steps of, a. passing the unwanted gas through a first bypass line around the large main gas line to the flare for detecting the gas flow slow flow rate portion of 1 percent to 3 percent of maximum design flow rate, b. passing the unwanted gas through a second bypass line around the first bypass line for detecting the gas flow very slow flow rate portion of up to 1 percent maximum design flow rate, and c. passing the unwanted gas through the main line for detecting any gas flow in the measurable flow rate range.
 8. A smokeless gas flare having an aspirating steam nozzle for mixing air with gas for burning wherein the gas flow has An immeasurable flow rate in a large main gas line to the flare, the immeasurable flow rate gas having a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare further comprising, a. a first bypass line means around an end of the main gas line for passing the gas flow slow flow rate portion of 1 percent to 3 percent of maximum design flow rate, b. a second bypass line means around an end of said first bypass line means for passing the gas flow very slow flow rate portion of up to 1 percent maximum design flow rate, c. first means on said first bypass line means for detecting gas flowing at the slow flow rate, d. second means on said second bypass line means for detecting gas flowing at the very slow flow rate, e. means responsive to said first means for adding an empirically determined fixed set amount of steam for providing a smokeless flame, and f. means responsive to said second means for adding a second empirically determined fixed set amount of steam for providing a smokeless flame.
 9. In a gas flare for burning gas that has passed through a liquid separator including a container of liquid and gas wherein the main gas supply line protrudes well below the surface of the liquid for preventing flame travel in the gas line and wherein the gas flow has an immeasurable flow rate in the main gas supply line to the flare, the immeasurable flow rate gas having a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, means for detecting the flow rates comprising, a. a first bypass line between the main gas supply line and the container, b. a second bypass line between the first bypass line and the container, c. said first bypass line having means for detecting gas at the slow flow rate portion of 1 percent to 3 percent of maximum design flow rate, and d. said second bypass line having means for detecting gas at the very slow flow rate portion of up to 1 percent maximum design flow rate.
 10. A smokeless gas flare wherein the gas flow has an immeasurable flow rate in a large main gas line to the flare, the immeasurable flow rate gas having a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare further comprising, a. first means for detecting gas flowing at the slow flow rate of 1 percent to 3 percent maximum design flow rate, b. second means for detecting gas flowing at the very slow flow rate of up to 1 percent maximum design flow rate, c. third means responsive to said first means for adding an empirically determined fixed set amount of steam for smokeless burning of the slow flow rate gas, and d. said third means being responsive to said second means for adding a second empirically determined fixed set amount of steam for smokeless burning of the very slow flow rate gas.
 11. A smokeless gas flare as recited in claim 10 wherein, a. said first detecting means comprises an orifice run means on a first bypass line around an end of the large main gas line for detecting the slow flow rate portion of gas flow, and b. said second detecting means comprises an orifice run means on a second bypass line around an end of the first bypass line for detecting the very slow flow rate portion of gas flow.
 12. A smokeless gas flare as recited in claim 11 wherein an end of the large main gas line is submerged deep in a drum of liquid from which the gas is supplied to the flare and wherein, a. said end of said first bypass line is submerged shallower in said drum of liquid than the main gas line end for passing the slow flow rate portion of gas, and b. an end of said second Bypass line is submerged shallower in said drum of liquid than said first bypass line end for passing the very slow flow rate portion of gas.
 13. A smokeless gas flare utilizing aspirating steam for mixing air with gas for burning wherein the gas is supplied to the flare in a large main gas line and has a flow rate which is immeasurable in the large main gas line at times, the immeasurable flow rate gas comprising a slow flow rate portion of 1 percent to 3 percent of maximum design flow rate and a very slow flow rate portion of up to 1 percent maximum design flow rate, the flare comprising further, a. first means for detecting gas in the gas flow slow flow rate of 1 percent to 3 percent of maximum design flow rate, b. second means for detecting gas in the gas flow very slow flow rate of up to 1 percent maximum design flow rate, c. means for controlling aspirating steam flow to the gas flare for each of the ranges, and d. each of the steam flow controlling means being responsive to its respective detecting means for its range for maintaining a smokeless flame in the flare as the gas flow rate varies in the immeasurable flow rate portions.
 14. A smokeless gas flare as recited in claim 13 wherein, a. said first detecting means comprises an orifice run means on a first bypass line around an end of the large main gas line for detecting the slow flow rate portion of gas flow, and b. said second detecting means comprises an orifice run means on a second bypass line around an end of the first bypass line for detecting the very slow flow rate portion of gas flow. 